To improve our understanding of the response of tumore to hyperthermia we propose to quantitate changes in intralesional pO2 and pH during and following treatments with defined biological end points. In addition to investigating these changes in the C3H mouse mammary carcinoma model, identical studies will be performed in normal tissues to determine if differences in biological response (i.e., the therapeutic gain) can, in part, be attributed to differences in pO2 and pH changes. In all cases, determinations will be obtained during treatment, shortly after treatment when peak tissue reactions are observed and at later times during the recovery phase. At the completion of the single dose studies a series of experiments employing either fractionated hyperthermia or radiation plus hyperthermia will be conducted. During these more complex protocols, pO2 and pH changes will again be measured and documented. The results of these studies will provide evidence of the role of intralesional physiological changes on ultimate biological response to combined or fractionated treatments.